1. Core Biology Smart Teach 4: Genes and Inheritance

2. Key terms used in exam questions
Genes – Section of DNA that codes for an inherited characteristic eg blue eyes
Allelles – Different versions of the same gene eg B or b
Dominant – Allele always expressed even if only one copy, represented by captial letter eg brown eyes (B)
Recessive – Allele needs both copies to be expressed, represented by small letter eg blue eyes (b)
Genotype – The genes eg Bb
Phenotype – The physical charateristics eg blue eyes
Homozygous – Both alleles are the same eg BB
Heterozygous – Alleles are different eg Bb
Carrier – Has a recessive allele not expressed eg Bb carries the blue eyed gene
May need to expand on these definitions eg define the underlined words as well

3. What are the common themes in genes and inheritance?
Definitions
Crosses – Punnet Squares/Pedigree Charts
Genetic Diseases

4. Now lets have a look at some exam style questions about definitions..........

5. Q1. (3 marks = 3 minutes)  
State what is meant by the term heterozygous.
An allele is
    A  a single chromosome
    B  a single gene
    C  an alternative form of the same chromosome
    D  an alternative form of the same gene
State the genetic term used to describe an individual with the genotype ee for attached earlobes.

6. Answers
An individual who has one recessive allele and one dominant allele (1) OR 2 different alleles is acceptable. D
Homozygous recessive

7. How do we show how genes are inherited?
Punnet squares
Pedigree Diagrams

8. Punnet Square
The parents genotype will be given to you in the question so make sure you get the right way round. You will usually be told what letter to use as well but not always so choose a letter that you can clearly show the difference between a capital letter and a small letter.

9. Now lets have a look at an exam question about this..........

10. You could do this as a Walking Talking Mock style or let your class try to complete it individually.

12. The important part is the key because this will tell you who is affected and who is not.
You will not be asked to draw a pedigree chart, but you may be asked to interpret one eg how many females have albinoism? Ans: 0

13. Now lets have a look at an exam question about this..........

16. What are the two genetic diseases you could be asked about?
Sickle Cell Anaemia
Cystic Fibrosis
Note: They could mention other genetic diseases as examples but these are the only two that you do need to know the symptoms of.

17. Genetic diseases symptoms
Sickle Cell Anaemia
Misshapen red blood cells that can cause blood clots.
Pain in joints.
Tiredness.
Both of these diseases are recessive which means you need both copies of the faulty gene to have the disease.
They are inherited diseases which means they cannot be caught from someone like the common cold.
Cystic Fibrosis
Thick, sticky mucus leading to breathing and digestive problems.
More chest infections.
Less growth.

18. Now lets have a look at an exam question tying it all together..........

19. Genetic disorders and diagrams Question
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D to C
Walking Talking Mark
GCSE Biology (Legacy Specification)
Genetic disorders and diagrams Question
This is a narrated Walking Talking Mark slideshow.
It will run automatically when you press start slideshow from the beginning.
NB: Some of the QWC style questions have more marks than 6 available this is to allow for students to see all of the possible marking points.
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20. a. Mr and Mrs Livingstone are both carriers of cystic fibrosis.
Question a – Genetic disorders and diagrams
a. Mr and Mrs Livingstone are both carriers of cystic fibrosis.
What does the term “carrier” mean?
(2 marks)

21. a. Mr and Mrs Livingstone are both carriers of cystic fibrosis.
Answer a– Genetic disorders and diagrams
a. Mr and Mrs Livingstone are both carriers of cystic fibrosis.
What does the term “carrier” mean? (2 mark)
It means that each parent has an allele for the disease but they are not affected by it.
(In this case it is a recessive allele).

22. Question b – Genetic disorders and diagrams
b. The Livingstone's have three children, as shown in the family tree below.
By representing the normal allele as N and the allele for Cystic fibrosis as n, construct a genetic diagram in the space below to show how each of the genotypes of the children came about. Identify each of the children’s genotypes in your diagram.
(4 marks)

23. Mr L N n Mrs L NN David Nn (Ian) nn Heather
Answers b – Genetic disorders and diagrams
b. The Livingstone's have three children, as shown in the family tree.
By representing the normal allele as N and the allele for Cystic fibrosis as n, construct a genetic diagram in the space below to show how each of the genotypes of the children came about. Identify each of the children’s genotypes in your diagram.(4 marks)
Mr L N n
Mrs L NN
David Nn
(Ian) nn
Heather

24. Question c – Genetic disorders and diagrams
c. Myotonic Dystrophy is an inherited disorder. The diagram shows the inheritance of Myotonic Dystrophy in one family. Is Myotonic Dystrophy caused by a dominant or recessive allele? Explain your answer. (2 marks)

25. Answer c – Genetic disorders and diagrams
c. Myotonic Dystrophy is an inherited disorder. The diagram shows the inheritance of Myotonic Dystrophy in one family. Is Myotonic Dystrophy caused by a dominant or recessive allele? Explain your answer. (2 marks)
Myotonic Dystrophy caused by a dominant allele you can tell because 2 affected parents have unaffected child (parents 1 and 2 and children 5 and 6).